Category Archives: visualization

I’m working on a TOP SEKKRIT* project involving large-scale data mining of the psychology literature. I don’t have anything to say about the TOP SEKKRIT* project just yet, but I will say that in the process of extracting certain information I needed in order to do certain things I won’t talk about, I ended up with certain kinds of data that are useful for certain other tangential analyses. Just for fun, I threw some co-authorship data from 2,000+ Psychological Science articles into the d3.js blender, and out popped an interactive network graph of all researchers who have published at least 2 papers in Psych Science in the last 10 years**. It looks like this:

You can click on the image to take a closer (and interactive) look.

I don’t think this is very useful for anything right now, but if nothing else, it’s fun to drag Adam Galinsky around the screen and watch half of the field come along for the ride. There are plenty of other more interesting things one could do with this, though, and it’s also quite easy to generate the same graph for other journals, so I expect to have more to say about this later on.

* It’s not really TOP SEKKRIT at all–it just sounds more exciting that way.

** Or, more accurately, researchers who have co-authored at least 2 Psych Science papers with other researchers who meet the same criterion. Otherwise we’d have even more nodes in the graph, and as you can see, it’s already pretty messy.

If you’ve visited the Neurosynth website lately, you may have noticed that it looks… the same way it’s always looked. It hasn’t really changed in the last ~20 months, despite the vague promise on the front page that in the next few months, we’re going to do X, Y, Z to improve the functionality. The lack of updates is not by design; it’s because until recently I didn’t have much time to work on Neurosynth. Now that much of my time is committed to the project, things are moving ahead pretty nicely, though the changes behind the scenes aren’t reflected in any user-end improvements yet.

The github repo is now regularly updated and even gets the occasional contribution from someone other than myself; I expect that to ramp up considerably in the coming months. You can already use the code to run your own automated meta-analyses fairly easily; e.g., with everything set up right (follow the Readme and examples in the repo), the following lines of code:

…will perform an automated meta-analysis of all studies in the Neurosynth database that use the term ‘memory’ at a frequency of 1 in 1,000 words or greater, but don’t use the terms wm or working, or words that start with ‘episod’ (e.g., episodic). You can perform queries that nest to arbitrary depths, so it’s a pretty powerful engine for quickly generating customized meta-analyses, subject to all of the usual caveats surrounding Neurosynth (i.e., that the underlying data are very noisy, that terms aren’t mental states, etc.).

Anyway, with the core tools coming along, I’ve started to turn back to other elements of the project, starting with the image viewer. Yesterday I pushed the first commit of a new version of the viewer that’s currently on the Neurosynth website. In the next few weeks, this new version will be replacing the current version of the viewer, along with a bunch of other changes to the website.

A live demo of the new viewer is available here. It’s not much to look at right now, but behind the scenes, it’s actually a huge improvement on the old viewer in a number of ways:

The code is completely refactored and is all nice and object-oriented now. It’s also in CoffeeScript, which is an alternative and (if you’re coming from a Python or Ruby background) much more readable syntax for JavaScript. The source code is on github and contributions are very much encouraged. Like most scientists, I’m generally loathe to share my code publicly because I think it sucks most of the time. But I actually feel pretty good about this code. It’s not good code by any stretch, but I think it rises to the level of ‘mostly sensible’, which is about as much as I can hope for.

The viewer now handles multiple layers simultaneously, with the ability to hide and show layers, reorder them by dragging, vary the transparency, assign different color palettes, etc. These features have been staples of offline viewers pretty much since the prehistoric beginnings of fMRI time, but they aren’t available in the current Neurosynth viewer or most other online viewers I’m aware of, so this is a nice addition.

The architecture is modular, so that it should be quite easy in future to drop in other alternative views onto the data without having to muck about with the app logic. E.g., adding a 3D WebGL-based view to complement the current 2D slice-based HTML5 canvas approach is on the near-term agenda.

The resolution of the viewer is now higher–up from 4 mm to 2 mm (which is the most common native resolution used in packages like SPM and FSL). The original motivation for downsampling to 4 mm in the prior viewer was to keep filesize to a minimum and speed up the initial loading of images. But at some point I realized, hey, we’re living in the 21st century; people have fast internet connections now. So now the files are all in 2 mm resolution, which has the unpleasant effect of increasing file sizes by a factor of about 8, but also has the pleasant effect of making it so that you can actually tell what the hell you’re looking at.

Most importantly, there’s now a clean, and near-complete, separation between the HTML/CSS content and the JavaScript code. Which means that you can now effectively drop the viewer into just about any HTML page with just a few lines of code. So in theory, you can have basically the same viewer you see in the demo just by sticking something like the following into your page:

Well, okay, there are some other dependencies and styling stuff you’re not seeing. But all of that stuff is included in the example folder here. And of course, you can modify any of the HTML/CSS you see in the example; the whole point is that you can now easily style the viewer however you want it, without having to worry about any of the app logic.

What’s also nice about this is that you can easily pick and choose which of the viewer’s features you want to include in your page; nothing will (or at least, should) break no matter what you do. So, for example, you could decide you only want to display a single view showing only axial slices; or to allow users to manipulate the threshold of layers but not their opacity; or to show the current position of the crosshairs but not the corresponding voxel value; and so on. All you have to do is include or exclude the various addSlider() and addData() lines you see above.

Of course, it wouldn’t be a mediocre open source project if it didn’t have some important limitations I’ve been hiding from you until near the very end of this post (hoping, of course, that you wouldn’t bother to read this far down). The biggest limitation is that the viewer expects images to be in JSON format rather than a binary format like NIFTI or Analyze. This is a temporary headache until I or someone else can find the time and motivation to adapt one of the JavaScript NIFTI readers that are already out there (e.g., Satra Ghosh‘s parser for xtk), but for now, if you want to load your own images, you’re going to have to take the extra step of first converting them to JSON. Fortunately, the core Neurosynth Python package has a img_to_json() method in the imageutils module that will read in a NIFTI or Analyze volume and produce a JSON string in the expected format. Although I’m pretty sure it doesn’t handle orientation properly for some images, so don’t be surprised if your images look wonky. (And more importantly, if you fix the orientation issue, please commit your changes to the repo.)

In any case, as long as you’re comfortable with a bit of HTML/CSS/JavaScript hacking, the example/ folder in the github repo has everything you need to drop the viewer into your own pages. If you do use this code internally, please let me know! Partly for my own edification, but mostly because when I write my annual progress reports to the NIH, it’s nice to be able to truthfully say, “hey, look, people are actually using this neat thing we built with taxpayer money.”

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In the last year or so, I’ve been experimenting with different ways of displaying correlation matrices, and have gotten very fond of color-coded correlograms. Here’s one from a paper I wrote investigating the relationship between personality and word use among bloggers (click to enlarge):

The rows reflect language categories from Jamie Pennebaker’sLinguistic Inquiry and Word Count (LIWC) dictionary; the columns reflect Extraversion scores (first column) or scores on the lower-order “facets” of Extraversion (as measured by the IPIP version of the NEO-PI-R). The plot was generated in R using code adapted from the corrgram package (R really does have contributed packages for everything). Positive correlations are in blue, negative ones are in red.

The thing I really like about these figures is that the colors instantly orient you to the most important features of the correlation matrix, instead of having to inspect every cell for the all-important ***magical***asterisks***of***statistical***significance***. For instance, a cursory glance tells you that even though Excitement-Seeking and Cheerfulness are both nominally facets of Extraversion, they’re associated with very different patterns of word use. And then a slightly less cursory glance tells you that that’s because people with high Excitement-Seeking scores like to swear a lot and use negative emotion words, while Cheerful people like to talk about friends, music, and use positive emotional language. You’d get the same information without the color, of course, but it’d take much longer to extract, and then you’d have to struggle to keep all of the relevant numbers in mind while you mull them over. The colors do a lot to reduce cognitive load, and also have the secondary benefit of looking pretty.

If you’re interested in using correlograms, a good place to start is the Quick-R tutorial on correlograms in R. The documentation for the corrgram package is here, and there’s a nice discussion of the principles behind the visual display of correlation matrices in this article.

p.s. I’m aware this post has the worst title ever; the sign-up sheet for copy editing duties is in the comment box (hint hint).